1. Field of the Invention
The present invention provides an active device array substrate and fabricating method thereof. In particular, a method for fabricating a thin film transistor array substrate, which can reduce the number of required mask processes, is provided.
2. Descriptions of the Related Art
Liquid crystal displays (LCDs) possess several advantages, such as high definition, small volume, light weight, low-voltage drive, low power consumption, a broad range of applications, etc. Thus, LCDs have been widely applied in consumer electronic products, such as portable televisions, mobile phones, notebooks, desktop displays and the like and have also become mainstream in display markets.
A general liquid crystal display, like a thin-film transistor liquid crystal display, is essentially composed of a thin film transistor array substrate, a color filter array substrate and a liquid crystal layer. A thin film transistor array substrate is composed of a plurality of thin film transistors arranged in arrays and a plurality of pixel electrodes corresponding to each of the thin film transistors. The individual pixel units therein are usually controlled by a gate line and a data line.
However, with the trend of device miniaturization, a flattening process is typically used to produce a thin film transistor array substrate to provide a better aperture ratio on a smaller substrate area, in the traditional flattening process for producing a thin film transistor array substrate, five to six photolithography (or so-called “mask”) processes are usually necessary to produce the desired array substrate. Each of the photolithography processes includes the following steps: coating of a photoresist, the use of patterned masks, the exposure of the photoresist, the development of the photoresist, film etching, the removal of the residual photoresist, etc. These steps will be collectively referred to as the “mask process” hereafter.
When producing a thin film transistor active array substrate in prior art, the first mask process (where a binary mask is used) is firstly introduced to form a patterned first metal layer on the substrate, which serves as the gates, gate lines and gate pads. Secondly, the first insulating layer and semiconductor layer are deposited sequentially. A second mask process is then performed to define the patterned semiconductor layer on the first insulating layer above the gates. Subsequently, a second metal layer is further deposited and a third mask process is performed to pattern the second metal layer to form the sources/drains, storage electrodes, data lines and data pads. The second insulating layer is then deposited subsequently and a fourth mask process is applied to produce a plurality of openings with a suitable depth, which function as the contact windows for metals. Finally, a conducting layer is deposited thereon and a fifth mask process is utilized to pattern the conducting layer to form the pixel electrodes. The production of the thin film transistor array substrate is then completed herein. In some conventional methods, after the second metal layer is patterned, a protection layer may be additionally deposited before performing another mask process. Therefore, six mask processes are involved, as mentioned in U.S. Pat. No. 6,862,070 B1.
As aforementioned, at least five mask processes have to be adopted according to prior arts of producing array substrates. However, this producing method is highly complicated, and each mask pattern has to be aimed precisely. Particularly, with the trend of the devices miniaturization, the difficulty of a whole process will be higher if many times of the aim of patterns are involved therein. If the deviation of aim occurs in any single mask, the produced device will deviate from the original design, and the efficiency of the device will significantly decrease, thus causing the deterioration of yields and the increase of costs. Hence, to develop a novel technique, which can decrease the number of the use of masks and maintain the high performance of liquid crystal displays, is desperately required in industry.
On the basis of the aforesaid descriptions, the inventor of the present invention provides a method for producing an array substrate, which can still provide an array substrate with favorable performance on the premise of decreasing the number of masks to lower the costs.